Positron Emission Tomography (PET) is a nuclear medicine medical imaging technique which produces a three-dimensional image or map of, for example, functional processes in the body. The system detects pairs of gamma rays emitted indirectly by a positron-emitting radioisotope, which is introduced into the body on a metabolically active molecule. Images of metabolic activity in space are then reconstructed by computer analysis. Scanners may be aided by results from a CT X-ray scan performed at the same time in the same machine.
One of the many challenging aspects of developing positron emission tomography (PET) instrumentation is the thorough validation of coincidence-event data acquisition systems. The multiple random processes at work in the PET portion of PET/CT make for unusually subtle problems in electronic data acquisition. These random processes are difficult to reproduce without actually using an expensive array of PET detectors and physically handling radio-active sources. These challenging processes include: random order of packet arrival (emission in random 3-D directions by the always-180-degree-opposed gamma pairs), random arrival times of coincidence-event packets (Poisson-distributed), and dynamically changing rates of packet arrival (biological movement, e.g., cardiac and respiratory and nuclear half-life of injected tracers such as F-18, Rb-82.) Often, there is the added health burden to personnel due to the frequent handling of these sources. This handling is perhaps more easily accepted when an actual patient is involved but harder to bear when repeatedly loading “phantom” source containers just to validate a minor change in the “under-test” PET data acquisition system. Obviously, the non-trivial capital investment required of current PET/CT equipment means there is seldom any supplemental access to real PET detector arrays for the purpose of development and test. In total, these technical and fiscal challenges tend to significantly slow the rate of advancement to the state of the art in PET.